Hallo,
am Waiblinger Usertreffen hatte ntrs_france eine wenig bekannte C64 Variante dabei. Ein "Procep C64". Ein C64 mit interner Erweiterungsplatine zur Erzeugung eines RGB-Ausgangssignals. Das wurde Frankreich so verwendet, da zu der Zeit als TV-Norm SECAM eingesetzt wurde und der Videoausgang des C64 dazu inkompatibel ist. Leider war der Rechner defekt, aber ich habe mich nun mal drangesetzt. Die technischen Details beschreibe ich auf englisch damit ntrs und Freunde das besser lesen können.
C64 mainboard 250425 with Procep ATV PAL-RVB 14-03-54 attached to a Commodore 1085S monitor - only RGB input
(SID removed for protection whilst repair)
Procep PAL to RGB converter unit
Repair of a dead unit: Procep C64 with ATV PAL-RVB 14-03-54 board and RGB (RVB) output
For the dead unit, it was not sure if the fault is in the C64 part or in the RGB converter. The C64 mainboard is a common 250425 assembly. But several wires were soldered to it, to supply the procep board with power and input signal, and to put the RGB signal to the normal video outlet. (Changed pinout, dangerous)
My first step was to divide the system in two parts for repairing the normal C64 mainboard. The C64 had a problem before, and on the RGB converter, there was a burnt resistor between the two electrolytic capacitors.
Overview. Left: orange/black power wires / Middle: Signal input and modification to get composite (FBAS) from the board), above video plug socket modification
Video plug socket. Several wires were cut on the board for changing the signal.
Needed modification for PAL composite (FBAS) output. The green wire fixes a cut before the modulator, and the red/blue marks show were the composite signal can be obtained.
With this modification, it was possible to handle the C64 as a normal repair and use normal video for testing. The problem of the board were 2 defective 4164 RAM chips.
For checking the Procep RGB board, a cable was needed. The Pinout is
AudioVideo_8pol_Pinbelegung.gif
Pin 2 GND
Pin 4 CSync
Pin 6 GREEN
Pin 7 RED
Pin 8 BLUE
Pin 1 +12V (!) (not needed)
This can be easily connected to a DB9 plug for Commodore Monitors. 1085 DB9 Pinout
With that cable, the computer worked. Video output is quite good.
But some questions remain open. The burnt resistor. Seemed to have gotten a bit hot. It seems that the power supply wiring with the two capacitors is type of a Greinacher circuit. It supplies a 2812 (7812 compatible). The resistor has 6,4 ohm. In case of overload, which easily happens when the +12V output on the video outlets gets shortend, it will burn. The few pictures of the board on the net show the same sympton, by example visual here:
The resistor there had also overheated.
To complete this, it is an interesting type of C64. The text shall show the needed steps which make a repair easier, not specific detail of the many possible C64 faults. About the modulator board, it would be nice if anybody has more information or even schematics from it.
Regards
Andreas
